Router v client: don't assume that the router's DNS settings take precedence over the device's. That's only true if the client (Windows, say) is set up to 'Obtain DNS Server automatically'. Any manual setting on a device will over-ride the router on that interface, for instance Wi-Fi/wired.
Mobile devices: changing DNS servers on mobile platforms such as Android is more complex than for a PC. Android allows users to do this for Wi-Fi, but it will only remember the setting for that network, for example when a user is at home or work. It also requires the user to set a static IP address so no DHCP. There are a couple of apps to help with this on Android, DNS Changer and DNSet. Unfortunately, this approach can't be extended to 3G or 4G without root access - carrier access still requires accepting the default DNS.
IPv6: public IPv6 servers are also offered by the following providers but it's best to steer clear of them for now.
Privacy: most of the services described below promote themselves on filtering security which inevitably means they are gathering data on websites visited. You could argue that this is true of all DNS systems, including those from the ISPs that most people use quite happily. But it is not always clear where this data is stored nor what use it might be put to by those collecting it. Information is valuable in today's Internet economy so be aware that a 'free' service might have hidden privvacy downsides.
Top 6 free DNS services 2016 - public DNS services
Google. Easy to remember for IPv4 on 184.108.40.206 with its backup on 220.127.116.11, users will expect and get high availability a lot of filtering and security such as DNSSEC as standard. Since Google's business is advertising, it's very much a one size fits all model with no configuration to speak of. The standard-setter for public DNS, Google is one of the fastest too. Google collects data on users as it does from all its services although in the case of DNS it should be impersonal. If you can put up with that, this is definitely the one to beat.
OpenDNS. Now part of the Cisco empire, the primary is 18.104.22.168 with a backup on 22.214.171.124. Home users can simply adjust their DNS to point at one of the above but OpenDNS also offers the service wrapped up in three further tiers of service, Family Shield, Home, and VIP Home, the latter having a subscription fee of $19.95 (£14) per annum. These come with varying levels of filtering and security, including parental control, anti-phishing protection and, on the subscription tier, web whitelisting.
Norton ConnectSafe. Available in its basic form on 126.96.36.199 (backup 188.8.131.52) with other servers specified to filter content such as porn, file sharing, abortion, mature content. Also offered asNorton ConnectSafe for Business.
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